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Alameda Point Explained: A plan to stem the tides

Alameda Point Explained: A plan to stem the tides

Michele Ellson

Friday, September 6, 2013 - 00:05

This rocky revetment protects the shoreline along Seaplane Lagoon. Photo by Michele Ellson.

Updated at 10:32 a.m. Friday, September 6

One of the many challenges to be faced by the city and developers seeking to revitalize Alameda Point will be rising seas. The Intergovernmental Panel on Climate Change last estimated that the world’s mean sea level could rise by between 7 and 23 inches by 2099 (new estimates are due in just a few weeks); state-level estimates put sea level rise on California’s coasts as high as 69 inches by the turn of the next century.

A draft environmental study and a separate plan for rebuilding the Point’s roads, drains and utilities anticipates the waters that surround much of the Point rising by as many as 55 inches over the next 100 years; that’s not including wind-induced and once-a-century high tides that could lift waters an additional 3.6 feet.

Both documents outline a series of near- and long-term strategies for protecting existing structures and future development from rising tides, strategies that include creating higher ground, building levees and floodwalls and if all else fails, ceding some of former Naval air station back to the Bay.

But protection from rising waters won’t come cheap. The infrastructure plan estimates the cost of flood protection and site grading – piling tons of dirt on top of the existing site to lift it further from the water – will cost close to $110 million (that amount includes money to stabilize the shoreline); replacing the former Navy base’s storm drains will cost another $32.9 million. Taken together, that’s a substantial chunk of a newly estimated $567 million cost to repair and replace the Point’s roads, drains and utilities.

In the past, those fixes would have been funded at least in part by the future property tax revenues development at the Point would generate. But now, city leaders will contemplate setting up a special assessment district into which the Point's residents and businesses would pay fees for flood protection.

The draft infrastructure plan proposes an initial flood protection system that would lay close to 1.8 million cubic yards of dirt to elevate parts of the former base that are slated for new development by five to six feet. The area where buildings are slated for reuse – some of which would be inundated if century-high tides and a foot and a half of water rise come to pass – would be protected by a series of seven-foot-high levees and floodwalls designed of ward off those waters plus storm surges while the storm water system that serves it is upgraded.

The area of the base that rings Seaplane Lagoon is now protected by sloping, rocky revetments and a concrete wall that could be raised to safeguard a waterfront promenade and other hoped-for development there; protection for some of the more wind-impacted portions of the lagoon may extend as tall as nine feet. Alameda Point Chief Operating Officer Jennifer Ott said the city is working with a design firm to figure out what that could look like and that the city isn’t planning to wall any part of the Point off.

A planned extension of the Bay Trail is also expected to help protect the Point. Plans for the trail show it topping a berm that could be as high as 10 feet tall.

Meanwhile, low-lying Main Street could be raised by 3.6 feet to protect it from inundation if a big tide hits.

If the Bay and Oakland/Alameda Estuary rise beyond these early projections, the plan adds levees and floodwalls around new development areas and raises the ones protecting buildings that are being reused to withstand a sea level rise of up to 55 inches. Those barriers could also be pushed back between 50 and 100 feet – land would be set aside for a water-enforced retreat from the shore – and protective tidal wetlands installed in their place.

That extra sea level rise - and the need to bolster the Point's defenses against it - could mean a move for some existing features, like the Main Street dog park and adjacent parking lot.

“It’s not a big deal to move it, in the scheme of things,” Ott said.

The draft infrastructure plan and Alameda Point Project Environmental Impact report are both here.

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